UNITED STATES DEPARTMENT OF THE INTERIOR Harold L. Ickes, Secretary GEOLOGICAL SURVEY W. C. Mendenhall, Director Bulletin 931-Q QUICKSILVER AND ANTIMONY DEPOSITS OF THE STAYTON DISTRICT, CALIFORNIA BY EDGAR H. BAILEY AND W. BRADLEY MYERS Strategic Minerals Investigations, 1941 (Pages 405-434) UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1942 For Bale by the Superintendent of Documents, Washington, D. C. ------- Price 40 cents CONTENTS Page Abstract.............. '. .................. '. ................. 405 Introduction............. : ................................ 405 History and production...................................... 407 Geology.................................................. 408 Pre-Tertiary rocks................................... 409 Franciscan .(Jurassic?) and Cretaceous (?) rocks.-. 409' Serpentine....................................... 410 Tertiary igneous rocks.................................. 411 Basaltic extrusive rocks......................... 411, Andesitic extrusive rocks........................ 412 Andesitic intrusive rocks........................ 413 Rhyolitic intrusive rocks ........................ 413 Faults.. ............................................. 414 Ore deposits............................................. 415 Antimony veins........................................ 415 Quicksilver deposits................................. 416 Mineralogy.............................'............... 417" Paragenesis.......................................... 419 Origin and localization.............................. 419 Reserves................................................. 421 Antimony............................................... 421 Quicksilver........................................... 421 Suggestions for prospecting.............................. 422 Description of mines...................................... 423 Antimony mines........................................ 423 Ambrose mine..................................... 423 Blue Wing mine................................... 4'25 Shrlver mine..................................... 426 Quicksilver mines.................................... 426 Stayton mine..................................... 426 Yellow Jacket mine...............................' 429 Gypsy mine........................................ 430 Comstock mine.................................... 431 Marlposa mine.................................... 433 ILLUSTRATIONS Page Plate 64. Geologic map and sections of the Stayton min­ ing district, California................. In pocket 65. Geologic map and section of the upper levels of the Stayton mine,- Merced County, Calif.................................... In pocket* 66. Geologic map and sections of the Gypsy mine, Merced County,. Calif.................. 432 67. Geologic map and section of the Comstock mine, Santa Clara County, Calif................... 432 III IV ILLUSTRATIONS Page Figure 46. Index map of southern California showing the location of the Stayton district and the approximate extent of the Miocene (?) vol­ canic field. ................................ 406 47.' Geologic map of the Ambrose mine.............. 424 48. Geologic map of the Yellow Jacket mine........ 429 49. Geologic map of 'the Mariposa mine............. 434 QUICKSILVER AND ANTIMONY DEPOSITS OF THE STAYTON DISTRICT, CALIFORNIA By Edgar H* Bailey and W. Bradley Myers ABSTRACT The Stayton district, which lies 13 miles northeast of Hoi- lister, Calif., includes parts of San Benito, Santa Clara, and Merced Counties. The district has yielded about 1,700 flasks I/ of quicksilver, mostly between 1870 and 1880, and a .few tons of antimony ore. The rocks of the district include Jurassic (?) (Franciscan formation) and Cretaceous (?) sedimentary rocks, serpentinlzed ultrabasic rocks intruded into the Franciscan rocks, Miocene (?) basaltic and andesitic extrusive rocks, and several intrusive bodies of Miocene (?) andeslte and rhyolite. The basaltic ex­ trusive rocks were arched into a northward-trending asymmetrical anticline, then planed by erosion and capped by the andesitic rock. All the rocks are cut by northward-trending faults along which there have been several periods of movement. Veins containing stibnlte occur mainly in the basaltic rocks along faults in the central part of the' district. They are es­ timated to contain several tens of thousands of tons of poten­ tial ore averaging about 1^ percent of antimony. Cinnabar, the only commercially important quicksilver miner­ al, has three different modes of occurrence: (1) Veins and coatings in fractures in broken antimony veins, (2) coatings on otherwise unmineralized fractures in basalt, and (3) veins and replacement deposits in silica-carbonate rock derived from ser­ pentine. The possible reserves of the five largest mines amount to slightly more than 1,000 flasks of quicksilver. The largest mine, the Stayton, is probably capable of producing nearly 100 flasks per year for a few years. Additional prospecting along broken antimony veins immediately below the contact, between the two volcanic units might uncover additional deposits of medium- grade quicksilver ore. INTRODUCTION . The Stayton quicksilver and antimony district is on the crest of the Diablo Range 90 miles southeast of San Francisco and 13 miles northeast of Holli'ster, California (fig. 46). I/ A flask contains 76 pounds. 406 STRATEGIC MINERALS INVESTIGATIONS, 1941 It is in Tps. II and 12 S., R 0 7 E., in the northwestern corner of the Quien Sab.e quadrangle. ' The'district lies mostly in northeastern San Benito County, but .it also includes parts of southeastern Santa Clara County and western Merced County.. The only good road into the district extends from Hollister, on the Southern Pacific Hailroad, to the Stayton mine, which is the 38° Figure U6. Index map of southern California showing the location of the Stayton district and the approximate extent of the Miocene (?) volcanic field. Solid black shows*area mapped; ruled area shows volcanic field. largest in the district; other roads are passable only during the dry summer months 0 Little geologic work has been done hitherto in the .region. 2/ 3/ Becker -' briefly mentioned the mines, and Forstner -'made a reconnaissance map of the area in 1903. 2j Becker, G. F., Geology of the quicksilver deposits of the Pacific slope: U. S. Geol. Survey Won. 13, p. 380, 188S. ^/ Forstner, William, The quicksilver resources of California: Califor­ nia Min. Bur. Bull. 21, pp. 12S, l^T-lUg, 1903. QUICKSILVER AND ANTIMONY, STAYTON DISTRICT, CALIF, 407 The field work furnishing the basis for this report was done during approximately 2 months in' the spring of 1941. The areal geology was plotted on airplane photographs and later fitted to photographic enlargements of the Quien Sabe topographic sheet. The operators and miners in the- district, especially Mr. Ro B. Knox, owner an'd operator of the Stayton mine, were uni­ formly courteous and helpful*. The writers are indebted to E. B. Eckel of the Geological Survey for advice during the field work and the preparation of this report. HISTORY AND PRODUCTION The veins of the Stayton district were mined for antimony when first worked, between 1870 and 1875, but the more valuable cinnabar was soon discovered,, By 1876 the Stayton Mining Co 0 had gained control of the Gypsy, Stayton, and several smaller mines, and the company is reported !/to have produced about 1,000 flasks of quicksilver before 1880. The Comstock mine in the northern part 'of .the district was also discovered in the seventies and produced about 300 flasks .prior to 1880. The production of .the district from 1880 to 1920 is not known but is believed to have been very small. An accurate record is available only for the Stayton mine, which has produced 390g- flasks since the revival of mining in 1920. Production of quicksilver, in flasks, from the Stayton mine, 1920-40 I/ 1920...o.................. 17 1932...........o.......... 9 1921...................... 10 1933...................... 12 1922....... ................ 1934...................... 1 1924*..................... 5 1935...................... 18 1927... .................... 20 1936...................... 9 1928...................... 85 1937...................... 11 1929.o.................... 78 1938...................... 18 1930...........o.......... 60 1939...................... 10 1931...................... 14 1940...................... 13 Total................. 390^ I/ From records of the California State Mining Bureau. Published with the permission of Mr. R. B. Knox. }j/ Porstner, William, op. cit., p. 408 STRATEGIC MINERALS INVESTIGATIONS, 1941 The total quicksilver production of the district prior to 1940 is summarized in the table below. Quicksilver Mine Years (flasks) 1870-1880 300 1 R70-1 QT Q (?) 1,000 1920-1940 390 (?) 1,690 The amount of antimony produced is unrecorded, but the total probably is only a few hundred tons. GEOLOGY The Stayton district is underlain chiefly by Tertiary igne­ ous rocks, for it lies in the north-central part of a dissected Tertiary (Miocene?) volcanic field, which extends over an area of about a hundred square miles (fig. 46). Exposures of pre- Tertiary rocks are relatively small, and lie mainly in the low­ est canyon bottoms and around some volcanic plugs that have up­ turned the invaded rocks, as is shown on the geologic map of the district (pi. 64). Parts of the district are covered by Quater­ nary landslides and alluvial deposits; these require no further mention. The pre-Tertiary rocks were divided for mapping